Synthesis of vitamin a



Patented Dec. 16, 1947 UNITED STATES PATENT OFFICE 2,432,921 SYNTHESIS OF VITAMIN A Nicholas A. Milel'sf'Belmont, Mass, assignor to Research Corporation, New York, N. Y., a corporation of New York No Drawing; Applicationllune 20, 1944, Serial No. 541,293

2 Claims. (01. 260-468) 'fThis invention relates to a method for the Compound IV is then saponified in the presence synthesis of vitamin A and to certain interof alcoholic potash to give the tri-oarboxylic acid mediate products thereof. Compound V, H n .o q

The process may be regarded as starting with alcoholic t the compound having the formula V n OompoundIV CH3 CH3 H30 CH3 v CH; 01 0H3 cooH CH3 H H 1 H H H i H H 0=o-0==e-q=o H o= o-0:o- 3 ==OHC 0 0H 0 oooH H CH3 7 --H CH3- H2 t n 0 d M r Y -CompoundV r. I ompoun When CompoundV is heated m an mert at although, as will be apparent, the nt es m mosphere in the presence or absence of an orbecarrled on from any of the intermedmtepm r ganic base suchaS pyridine or powdered metallic ucts regardless of how they may have been Pm copper it is decarboxylated to Compound VI. pared. v t.

In my complete process starting with Com- Compound; pound I, the first step is to condense Compound Heat I with malonic ester in the presence of an alco- H30 1 7 belate such as magnesium or lithium aicohoiate H 11% N H2 Compound 11, as fOHOWSZ v H O=C-C=G; C .ICHT C=CH COOH oo0c1H5 P y 1 t i H t oooour-x v Gompoundl V I OompoundVI Mgormwgzm) When Compound VI is esterified and subse- OH r quently reduced wrth alumlnum iso-propylate H CH3 H E 00002; Compound VIIIresults. H O=C(\J:C-CC Compound VI esterifieation o OOOCH I H3O 0H2 Hz CH3 z 5 V H H H CH3 1 H c=oc=o-c-cHr-e=oH-c0002115 Compound II t r g t t In the second step Compound 11 is condensed H CH; with ethyl tetrolate (Compound III) in the presr r 1 '1 un ence of sodnrlr; :Ezgho} 21221;; g ve C ompo IY 40 Compound VII Coflpound III)2 a Al(isopropy1ate)z Compound 11 CompoundVII --r NaOC2H5 H8O CH 3 CH3 0H 'COOCH OH H H H H H H v H 1 n 2 5 H C=GsC-O-CH-. :CHk-COOC H; H C=C-C--=G-C-(\)---C==C-C'OOQ2H5 H p o COOOBHfi H OH; H CH: H 1 I I Compound W V o Compound YIII SOClz+pyridine Compound VIII orp-toluene sulphonic acid or (COOH): HaC CH3 CH CH3 H H I H H H 5 H C=C-C=CC=C =CH-COOC H H2 CH Compound IX.

Compound IX may be more simply prepared by reducing Compound IV with aluminum isopropylate to form Compound IVA reduction Compound IV aluminum iso-propylate C O Q C2H5 CH3 CH3 CH3 CH3 H H (1} H H I H H C=C =-CC(|]C=CC O 02115 I )11 C O O CZHE H2 CH3 Compound IV-A.

Then Compound IVA is saponified with alcoholic potash and the hydroxy tri-carboxylic acid formed is decarboxylated in the presence of pyridine. This latter operation simultaneously dehydrates the hydroxy acid to form the acid Compound IV--B.

decarboxylate and saponification dehydrate Compound IVA alcoholic potash pyridine CH3 CH3 CH3 CH3 H H H H H H H C=C =CC=C =C-COOH H CH3 Compound IVB Compound IVB can easily be converted to Compound IX by the methods of esterification described in more detail hereinafter.

Compound IX may be converted to vitamin A by treating it with excess hydrogen calcium bromide, thereby producing the desired alcohol or vitamin A.

Vitamin A may also be produced from Compound IVB by making first the corresponding um bromide or hydrogen calcium bromide or iodide.

A shorter procedure for the preparation of ompound With Compound X in the presence or lithium alcoholates.

CZH O 0.0 CHa EI(I3;CHC 0 O C2Hs 0211 0 00 (Compound X) Compound I Com ound IV Mg(0 03115) or LiOCzHs p the ethyl group.

The following are detailed descriptions of the steps briefly outlined above.

Condensation of the acid chloride, Compound I,

with diethyl malonate Magnesium alcoholate is made by refluxin a of absolute ethyl alcohol, 2 cc.

Condensation of Compound II with ethyl tetrolate-Compound III cooling to prevent rapid reaction, 15.6 g. of ethyl tetrolate (Compound HI).

temperature and distill under reduced pressure the excess ethyl tetrolate, leaving Compound IV.

The product, Compound IV, is a brown viscous liquid. It gives no ferric chloride reaction and has an absorption band the maximum of which is Saponzfication of Compound IV to the tricarboxylzc acid, Compound andthe-resulting mixture extracted three times.

with ether to remove any unsaponifiable material. The aqueous solution was then acidified with cold 10% orthophosphoric acid solution and the tricarboxylic acid extracted three times with ether; th extracts combined, washed several times with a; saturated-solution of sodium chloride and dried over magnesium sulfate. After the mixture was filtered and the ether removed under reduced pressure, the brown viscous tricarboxylic acid, Compound V, was subjected to a high vacuum (1 mm.) in an atmosphere of nitrogen for 3 hours at about 45 to remove any volatile materials. Partial decarboxylation occurred at this stage. Further decarboxylation of the product may be accomplished by heating at 1 mm. pressure for a longer time or at a higher temperature, e; g. for 4 hours at 60 C., for 5 hours at 95 C. and for 5 hours at 130 C.

A neutralization equivalent was taken of the product heated at 130 C. and found to be 300 as against 316, the calculated value.

A sample made via the c-methylw-carboethoxy glutaconic ester was decarboxylated in the same manner and gave identical results.

Decarboasylation of tricarbocrylic acid, Compound V, by pyridine to produce Compound VI To g. of tricarboxylic acid (Compound V) was added 8 cc. of anhydrous pyridine and the mixture allowed to stand overnight at room temperature. A solution of 63 cc. of 10% phosphoric acid was then added to the mixture with cooling in ice and the resulting mixture vigorously shaken until the odor of pyridine was no longer perceptible. Th mixture was then extracted with ether and the ether extract washed with Water and dried as before. The ether was removed under reduced pressure and the residue, Compound VI, subjected'to a vacuum of 2 mm. at (SO-70 for two hours.

The decarboxylation has also been accomplished by heating gently in the presence of metal lic copper powder.

Esterificution of Compound VI and subsequent reduction of the ketoester (Compound VII) to the hydroxyester (Compound VIII) Esterification ofth-e ketoacid (Compound VI) was eifected by four independent methods:

(1) by refluxing for 3 hours a mixture of the ketoacid (8.5 g.), absolute ethyl alcohol (8 00.), anhydrous copper sulfate (4.5 g.) and sulfuric acid (0.2 00.);

;(2) by heating at 150 for 24 hours in a sealed tube the silver salt (2.23 g.) of the ketoacid with ethyl iodide (33.)

(3) by making the acid chloride of the ketoacid (8.5 g.) in dry benzene with phosphorus trichloride (9 g.) cooling to 0 to remove phosphorus acid, and removing benzene and excess phosphorus trichloride under reduced pressure and reacting the residue with a solution of absolute alcohol (10 cc.) in 25 cc. of dry pyridine;

(4) by treating the sodium salt of the ketoacid with diethylsulfate.

In all cases the product, Compound VII, obtained had the expected analysis. The ketoester, Compound VII, exhibits an absorption band the maximum of which is in the region of 2800 A.

The reduction of the ketoester (Compound VII) was accomplished by means of aluminum isopropylate. About 4 g. of the ketoester was recc. of 2.0% acetic acid, the mixture extractedwith ether and the ethereal solution washed first with a 10% solution of sodium bicarbonate, then with water and sulfate.

The product gave a Zerewitinoff number corresponding'closely to one active hydrogen.

Dehydration. of Compound VIII Compound IX ries over the water formed into the distillate.

purified by removing the A The residue is then p-toluene sulfonic acid with a, 10% solution of sodium carbonate. The ester (Compound IX) is then extracted with ether and when the ether is removed the residual highly viscous product has the properties and analysis corresponding to the formula of Compound IX.

The dehydration of Compound VIII to produce Compound IX may also be accomplished bymaking the para-toluene sulfonic ester of this compound by reacting it with para-toluene sulfonyl chloride in pyridine, then'subsequently reacting the sulfonic ester with alcoholic potash. This reaction tends to remove para-toluene sulfonic acid rather than hydrolyzing the sulfonyl group thereby producing the conjugated acid which can be esterified to produce Compound IX. The dehydration may also be accomplished by refluxing Compound VlII in the presence of nitrogen with pyridine and thionyl chloride. This again has the, ability to chlorinate and dehydrochlorinate the hydroxyl group thereby producing the ester and Compound IX.

The Compound by heating it with anhydrous oxalic acid.

Reduction of the Icetotriester (Compound produce the hydroxytriester Compound 'IV--A Hydrolysis of Compound IV-A and subsequent decarboxylation of the tricurbomylic acid to produce Compound IV-B The hydroxytriester (Compound IV--A (3 g.) was hydrolyzed by heating it on the water with alcoholic potash (10%) pouring the mixture into 2 volumes of water, extracting with ether to remove any non-saponifiable material, acidifying the aqueous layer with phosphoric acid (10%) and extracting with ether the liberated tricarboxylic acid. When this acid is subjected to the pyridine decarboxylation as in the case of the decarboxylation of Compound V, the product dehydrated and decarboxylated at the same time to form the monocarboxylic acid (Compound finally dried over magnesium After filtration, the ether was removed and the residue, Compound VIII, subjected to high vacuum (2 mm.) to remove volatile substituents."

to produce VIII may also be dehydrated esterification described for Compound VI.

The reduction of Compound IX to produce vitamin A of the ester Compound IX is reacting it in anhydrous ether The reduction hydrous magnesium sulfate. When the ether is removed under reduced pressure the residue exhibits the properties of vitamin A.

Conversion of Compound I VB to vitamin A Compound IVB is first treated in anhydrous benzene at with an of phosphorus trichloride, then the mixture is heated at 40 for one-half hour. Cool the mixture to 0 ether, th magnesium sulfate. moved, the residue exhibits vitamin Compound I with Compound X Into 150 cc. of absolute alcohol dissolve 1.5 g. lithium metal and add to it slowly 46.2 g. of betamethyl-' carboethoxy glutaconic 40 hours, then refluxed gently on Dilute acetic acid was then added until the mixture was defi- This application is a continuation-in-part of my application Serial No. 413,233, filed October 1, 1941, now Patent No. 2,369,158.

I claim:

1. As a formula H3O CH3 COO alk CH3 CHa in which alk stands for an alkyl group.

2. Process which comprises condensing a compound of the formula in which X stands for of the formula a halogen with a compound alkO O C\% CH alkO O C in which alk stands for an alkyl group and Z stands for a metal of the alkali groups and condensing the resulting compound having the formula HaC CH3 OHa with a compound of the formula CH3CECC0Oalk in which all: stands for an alkyl group.

NICHOLAS A. MILAS. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,677,123 Adams July 17, 1928 2,101,217 Hill et a1 Dec. 7, 1937 2,228,256 Christiansen Jan. 14, 1941 2,200,306 Schneider May 14, 1940 new product a compound of the 

